For many years, attempts have been made to reduce CO2 emissions from blast furnaces so as to contribute to the general worldwide reduction of CO2 emissions.
Mainly in order to reduce the amount of coke used, a suggestion was made to recover the top gas from the blast furnace and to inject it back into the blast furnace to aid the reduction process. Devices have been proposed for separating the recovered top gas into a CO2 rich gas for use or storage elsewhere and a CO2 poor gas for injection back into the blast furnace so as to allow the reduction of coke.
Top gas can be reformed by reducing its CO2 content, e.g. by a method wherein fossil fuel is added to the top gas to partially convert carbon dioxide and steam to form carbon monoxide and hydrogen, as suggested in U.S. Pat. No. 3,884,677. This process requires the top gas to be heated to a very high temperature, i.e. in the region of 1,800 to 2,000° C. in order to react with the fossil fuel and break down carbon dioxide. Partial burning of the top gas is necessary to achieve the required temperature.
A nowadays more generally accepted method for reducing the CO2 content in the top gas is by Pressure Swing Adsorption (PSA) or Vacuum Pressure Swing Adsorption (VPSA), as e.g. shown in U.S. Pat. No. 6,478,841. PSA/VPSA installations produce a first stream of gas which is rich in CO and H2 and a second stream of gas rich in CO2 and H2O. The first stream of gas is used as reduction gas and injected back into the blast furnace. The second stream of gas is removed from the installation and, after extraction of the remaining calorific value, disposed of. This disposal controversially consists in pumping the CO2 rich gas into pockets underground for storage. Furthermore, although PSA/VPSA installations allow a considerable reduction of CO2 content in the top gas from about 35% to about 5%, they are very expensive to acquire, to maintain and to operate and they need a lot of space.